Drive 3 is slower as drive 2 at homing in Z [Solved]

deckingman

@thwe I had assumed that the reason you wanted to home to Z max, was that you have a CoreXY and also wanted to be able to resume after power failure. For this, the axes have to be re-homed and as there is a print already on the bed, one can't home to Z min.

So there are reasons why you or someone else might might want to home to Z max using multiple switches. That's why I thought it important to try and resolve your issue rather than simply suggest alternative ways of homing which involve homing to Z min with a probe.

Speaking as a mechanical engineer myself, I prefer to use mechanical solutions that don't rely on electronics to compensate for what are essentially fundamental mechanical problems. But I appreciate that others may not have the resources, time, or skills needed to do that.

thwe

@deckingman : My first priority is definitely a perfect backbone of the mechanics.

My guides (mgn12) and ballscrews are aligned with dial gauge (parallelism and flatness) and it is paid attention to a clean and easy running.
The print bed (alu fine milled 300 x 300 x 8mm) will be resurfaced on a flat grinding machine before installation , etc.

All measures usually do not require a software correction. However, I would like to apply the procedure, which also is used in tool setting measuring machines.

Why? just to learn for me.

Of course, my baby is supposed to print someday, my granddaughter is already waiting for the first figures and a personal name tag for her schoolbag. But the current stage is used to craft, build, rebuild, annoy if something does not work and look happy when it works - and learn.

The aim is to create a mechanical system to look behind the scenes, the machines I've just used. These are the last 25 years of application development on injection molding machines, from whose evolution in the direction of electric drives my curiosity comes.

Conclusion: I do not always and absolutely necessary have to use it, but I can do it (such as your "Dynamic Force Canceling" which is very interesting and implemented great)

PS: Sorry for any grammatical mistakes and wrong expressions - my english is only as well as google translators allowed

thwe

@deckingman said in Drive 3 is slower as drive 2 at homing in Z:

@thwe Strange indeed. It seems like one of the Z motors isn't retaining it's mapping after the first homing. A couple of suggestions to try.

At the start and end of your home Z file, explicitly assign all axes to the configuration you have in config.g. So at the start of homeZ, put M584 X0 Y1 Z2:3 U3 E4 P3. Then remap the drives by using M584 X0 Y1 Z2 U3 E4 P4. Carry out the rest of the homing, then at the end of home Z, re-enter the original drive mapping in full - i.e. M584 X0 Y1 Z2:3 U3 E4 P3.

Try initially assigning U to a different but unused axis like say 5. So in config.g use M584 X0 Y1 Z2:3 U5 E4 P3. Then in homez do M585 Z2 U3 before homing Z and U, then put the mapping back to Z2:3 U5.

I've no real idea if either of these will fix the issue but worth a try?

So I tested all your suggestions - unfortunately without success.
the first call works well, all others as usual: U runs slower

deckingman

@thwe Hmmmmm - very odd.

Try running the list of commands that David (DC42) suggested in his post dated and timed 18 Nov 2108, 17:01, starting with M584 P4 then M92 etc. Make a note of all the values. Then home Z and run those commands again and note the values. Then home Z a second time and run those commands for the third time. See if there is any change in the values reported for Z and U.

thwe

When testing the above suggestion, I accidentally noticed that when homing again suddenly everything is running properly, but what was different?

Well, the command M584 P4 before any other G commands has allowed both engines to run properly.

Now I have only as a first command in my homez.g "M584 P4" and now everything runs as it should.

dc42

I'm glad you solved it.

The homez.g file you posted earlier starts like this:

; homez.g
; called to home the Z axis
;
; Drive 0 as X
; Drive 1 as Y
; Drive 2 as Z -> 1st Z-motor (left one, viewed from ahead) which is normal Z
; Drive 3 as U -> 2nd Z-motor (right one, viewed from ahead) which is now U
; Drive 4 as Extruder

G91 ; relative positioning

M584 Z2 U3 P4 ; Split Z into 2 (Z+U)

Are you saying that putting the M584 command before the G91 command is what fixed it?

thwe

@dc42 said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

I'm glad you solved it.

The homez.g file you posted earlier starts like this:

; homez.g
; called to home the Z axis
;
; Drive 0 as X
; Drive 1 as Y
; Drive 2 as Z -> 1st Z-motor (left one, viewed from ahead) which is normal Z
; Drive 3 as U -> 2nd Z-motor (right one, viewed from ahead) which is now U
; Drive 4 as Extruder

G91 ; relative positioning

M584 Z2 U3 P4 ; Split Z into 2 (Z+U)

Are you saying that putting the M584 command before the G91 command is what fixed it?

Yes, before "G91" as first line.

dc42

That's very strange, because I can't see any possible mechanism for the order of G91 and M584 making a difference. Are you sure that you didn't change anything else?

thwe

Actually, yes, but I will reset it for safety's sake again to reproduce the funny behavior
At the Weekend i will give feedback

dc42

Thanks, I'll wait for that feedback before I do the 2.02 release in case we can identify something that needs to be fixed.

thwe

So, tested again:

Turn on Duet Wifi - homez.g as in the appendix
G28 Z (via Button Home Z in the DWC)
Homing OK!
Moving in Z: G1 Z-10 (via button in the DWC)
G28 Z (via Button HomeZ in the DWC)
Homing OK!
Moving in Z: G1 Z-10 (via button in the DWC)
Edit homez.g -> set a semicolon before M584 P4
G28 Z (via Button HomeZ in the DWC)
Homing NOT OK! -> U slower as Z
Moving in Z: G1 Z-10 (via button in the DWC)
Edit homez.g -> delet Semicolon before M584 P4
G28 Z (via Button HomeZ in the DWC)
Homing OK! -> U as fast as Z

Thus, it is certain that only the first line of content "M584 P4" in homez.g prevents the strange behavior of the different speeds.

Only valid if the z-axis has already been homed. After a new start or reboot, the FIRST homing will always work, whether with or without the above line, until the second homing occurs.

for safety's sake again here my config.g
0_1542973940030_config.g

... and here the homez.g:
0_1542974052538_homez.g

deckingman

@thwe

Thomas,

I'm glad that you've found a cause and a work around. No doubt David will look further into the cause and come up with a solution in the firmware.

dc42

@thwe said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

So, tested again:

Turn on Duet Wifi - homez.g as in the appendix

G28 Z (via Button Home Z in the DWC)

Homing OK!

Moving in Z: G1 Z-10 (via button in the DWC)

G28 Z (via Button HomeZ in the DWC)

Homing OK!

Moving in Z: G1 Z-10 (via button in the DWC)

Edit homez.g -> set a semicolon before M584 P4

G28 Z (via Button HomeZ in the DWC)

Homing NOT OK! -> U slower as Z

Moving in Z: G1 Z-10 (via button in the DWC)

Edit homez.g -> delet Semicolon before M584 P4

G28 Z (via Button HomeZ in the DWC)

Homing OK! -> U as fast as Z

Thus, it is certain that only the first line of content "M584 P4" in homez.g prevents the strange behavior of the different speeds.

Only valid if the z-axis has already been homed. After a new start or reboot, the FIRST homing will always work, whether with or without the above line, until the second homing occurs.

for safety's sake again here my config.g
0_1542973940030_config.g

... and here the homez.g:
0_1542974052538_homez.g

Thanks!

Does it still work if you exchange the M584 P4 and G91 commands?

thwe

@dc42 :

Thanks!

Does it still work if you exchange the M584 P4 and G91 commands?

Yes, it does not matter if the M584 ...command comes before or after the G91 - with it work

thwe

@deckingman said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

@thwe

Thomas,

I'm glad that you've found a cause and a work around. No doubt David will look further into the cause and come up with a solution in the firmware.

I think so too, but the importance is not so high for this problem - who needs homing after a homing

deckingman

@thwe said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

@deckingman said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

@thwe

Thomas,

I'm glad that you've found a cause and a work around. No doubt David will look further into the cause and come up with a solution in the firmware.

I think so too, but the importance is not so high for this problem - who needs homing after a homing

Actually I quite often home Z repeatedly. I often swap hot end assemblies which changes the offset from the nozzle to the probe and find that the easiest way to adjust is simply to home Z, then raise the bed until it grips a thin piece of paper, edit the offset and re-home, repeat as necessary. Admittedly I haven't had the problem you had with multiple screws but someone else might in the future so it's good to find a solution, even if it might seem to be a small and rare problem.

dc42

@thwe said in Drive 3 is slower as drive 2 at homing in Z [Solved]:

@dc42 :

Thanks!

Does it still work if you exchange the M584 P4 and G91 commands?

Yes, it does not matter if the M584 ...command comes before or after the G91 - with it work

Thanks, I believe I've found the cause and I will implement a change in 2.02RC5 that I hope will fix it. It's to do with what happens when in M584 you reassign a driver to an axis that is initially not visible.

thwe

@dc42 : Unfortunately the update to 2.02RC5 has brought no solution, it has even become worse.
After start or reboot the z-homing is ok, every further homing now always runs with the mentioned problem, no matter if with or without "M584 P4" and whether before or after the G91

dc42

@thwe, I'm sorry to hear that. Added to my list to investigate again.

thwe

Thanks for the effort.
I'm now back to 2.02RC4 to take the next steps, it's not rushing.